The invention concerns a device for varying valve timing of gas exchange valves in an internal combustion engine, particularly a hydraulic camshaft adjusting device of a rotary piston type fixed on a drive-side end of a camshaft mounted in a cylinder head of the internal combustion engine while being generally configured as a hydraulic adjusting drive comprising:
a drive pinion connected in driving relationship to a crankshaft of the internal combustion engine and a winged wheel connected rotationally fast to the camshaft of the internal combustion engine,
said drive pinion comprising a hollow space defined by a hollow cylindrical circumferential wall and two side walls, a plurality of hydraulic working chambers being formed in the hollow space by a plurality of radial limiting walls,
a plurality of radial wings arranged on an outer periphery of a wheel hub of the winged wheel, said wings extending individually into the working chambers and dividing the working chambers into first and second oppositely acting hydraulic pressure chambers,
a selective or simultaneous pressurizing of the pressure chambers by a hydraulic pressure medium effects a pivoting or a fixing of the winged wheel relative to the drive pinion, and thus, of the camshaft relative to the crankshaft.
A generic hydraulic camshaft adjusting device of a rotary piston type is known from DE 197 45 908 A1. This device is fixed on the drive-side end of a camshaft mounted in the cylinder head of the internal combustion engine and is generally configured as a hydraulic adjusting drive. This device configured as a so-called vane-type adjusting device, generally comprises a drive pinion connected in driving relationship to a crankshaft of the internal combustion engine and a winged wheel connected rotationally fast to the camshaft of the internal combustion engine. The drive pinion comprises a hollow space formed by a hollow cylindrical circumferential wall and two side walls, four hydraulic working chambers being formed in the hollow space by four radial limiting walls. The winged wheel consequently comprises on the outer periphery of its wheel hub, four radial wings each of which extends into one working chamber of the drive pinion, so that the working chambers are divided into four first and four second oppositely acting hydraulic pressure chambers. By a selective or simultaneous pressurizing of these pressure chambers by a hydraulic pressure medium, a pivoting or a fixing of the winged wheel relative to the drive pinion is effected so that the camshaft is pivoted or hydraulically clamped relative to the crankshaft. The hydraulic pressure medium for this purpose is taken from the lubrication circuit of the internal combustion engine and routed through a pressure medium adapter arranged in extension of the camshaft in the cylinder head of the internal combustion engine, and through two separate pressure medium ducts extending in axial direction in the adapter and in the device, the pressure medium being supplied to and discharged from the individual pressure chambers through radial bores made in the wheel hub of the winged wheel.
A drawback of this prior art device is that the radial bores in the wheel hub which open into the individual pressure chambers of the device are relatively complicated and expensive to implement and, to avoid a malfunctioning of the device due to drilling chips, the bores have to be deburred and cleaned by high pressure washing. In most cases, the radial bores are additionally optically checked for cleanliness with special apparatus so that, due to the number of radial bores required in correspondence to the number of pressure chambers in the device, relatively high fabrication costs are incurred and disproportionately high capital investment is required for the necessary equipment and apparatus which disadvantageously increases the total manufacturing costs of such a device.
It is an object of the invention to provide a device for varying valve timing of gas exchange valves of an internal combustion engine, and more particularly to provide a hydraulic camshaft adjusting device of a rotary piston type in which the manufacturing costs and capital investment required for implementing the supply and discharge pressure medium ducts for the pressure chambers of the device are reduced to a minimum.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves its objects in a device of the pre-cited type by the fact that the supply and discharge of the hydraulic pressure medium to and from the pressure chambers of the device is effected through radial grooves that are made in the side walls of the drive pinion, first ends of the radial grooves open into the pressure chambers and second ends of the radial grooves open into further pressure medium ducts of the device, the radial grooves being sealed pressure medium-tight between their first and second ends by lateral surfaces of the wheel hub of the winged wheel.
In an advantageous embodiment of the invention, the radial grooves opening into the first pressure chambers of the device are made in one of the side walls of the drive pinion and the radial grooves opening into the second pressure chambers are made in the other of the side walls of the drive pinion. This simplifies the supply and discharge, described more closely below, of hydraulic pressure medium within the device to the respective radial grooves in the side walls. However, with an appropriately modified pressure medium supply and discharge, it is possible to make both the radial grooves opening into the first pressure chambers and those opening into the second pressure chambers only in one of the side walls of the drive pinion.
With regard to the fabrication costs of the side walls of the drive pinion, it has further proved to be particularly advantageous to make both the side walls with all their apertures and shaped portions without chip removal as stamped or stamped and drawn parts, and to make the radial grooves in the side walls likewise without chip removal, for example, by stamping or stamping and drawing combined with coining. Alternatively, it is, of course, also possible to machine the radial grooves into the side walls by milling. The side walls may also be comprised, for example, of an outer wall and an inner wall and be made as chiplessly stamped or stamped and drawn parts in which the radial grooves are coped out of the inner walls, the disadvantage, however, being the relatively high fabrication and material costs of this method of manufacture.
According to a further feature of the invention, in a preferred embodiment of the invention, the radial grooves in the side walls of the drive pinion are arranged so as to start in an already existing coaxial aperture of the side walls and extend radially in a straight line up to the level of the wing stop surfaces of the limiting walls of the drive pinion while being angularly spaced from one another in correspondence to the angular spacing of the wing stop surfaces of the limiting walls. The existing coaxial aperture of the side walls of the drive pinion in which the radial grooves start is configured in the camshaft-distal side wall preferably as a central bore, known per se, that is suitable for a fixing screw to pass through for fixing the device on the camshaft. When the device has been mounted, this bore is sealed pressure medium-tight by a screw cap. On the side wall nearer the camshaft, the coaxial aperture is likewise preferably configured as a central passage, known per se, that is suitable for allowing the passage of a fixing adapter between the device and the drive-side end of the camshaft, or the passage of the drive-side end of the camshaft itself. At its end nearer the camshaft, this passage forms a sleeve-like flange which is sealed pressure medium-tight relative to the cylinder head of the internal combustion engine by a shaft seal ring arranged on this flange. The angular spacing of the radial grooves from one another can be symmetric or asymmetric depending on a like or unlike configuration and arrangement of the limiting walls in the drive pinion. However, a like configuration and arrangement of the limiting walls in the drive pinion which makes possible a symmetric arrangement of the radial grooves in the side walls of the drive pinion is particularly advantageous because, then, the radial grooves in both side walls can be made absolutely identically. Irrespective thereof, the radial grooves in the camshaft-distal side wall always end parallel and directly next to the one wing stop surfaces of the limiting walls of the drive pinion, while the radial grooves in the side wall nearer the camshaft always end parallel and directly next to the respective other wing stop surfaces of the limiting walls of the drive pinion.
Finally, according to a last feature of the device of the invention, the hydraulic pressure medium for the device is taken from the lubrication circuit of the internal combustion engine out of the radial bearing of the camshaft in the cylinder head of the internal combustion engine. It is preferably routed through two annular channels made in the drive-side end of the camshaft and then transferred within the camshaft and the device through a plurality of radial bores of the annular channels into the aforementioned further pressure medium ducts that are connected to the radial grooves of the side walls of the drive pinion. In a specially preferred embodiment, these further pressure medium ducts are configured as separate axial channels formed by a pressure medium guide sleeve, known per se, surrounding the fixing screw. Pressure medium out of one of the annular channels of the camshaft is conveyed to and from the radial grooves of the side wall of the drive pinion nearer the camshaft along the outer surface of this guide sleeve and through further radial bores within the device. The pressure medium out of the other annular channel of the camshaft, in contrast, is conveyed along the inner surface of the guide sleeve into a hollow space for the head of the fixing screw of the device and from there, to the radial grooves of the camshaft-distal side wall of the drive pinion, and back. For this purpose, it is also possible to use a variety of other known embodiments of separate axial channels through which the hydraulic pressure medium from the annular channels on the drive-side end of the camshaft, or even from another pressure medium tapping point, can be supplied to the radial grooves in the side walls of the drive pinion from the lubrication circuit of the internal combustion engine or from a separate pressure medium circuit.
The device of the invention for varying valve timing of gas exchange valves in an internal combustion engine, particularly a hydraulic camshaft adjusting device of a rotary piston type, therefore has the advantage over prior art devices that the ducts for the supply and discharge of the hydraulic medium that open into the individual pressure chambers of the device have no longer to be drilled in a complicated and expensive manner in the wheel hub of the winged wheel but can be made as radial grooves without chip removal in the side walls of the drive pinion. Due to the chipless production of the pressure medium ducts, a cleaning of the radial grooves by high pressure washing and a subsequent optical check with special apparatus can be dispensed with, so that, due to the lower fabrication costs and capital investment, the total manufacturing costs of a device of this type are substantially reduced.
The invention will now described more closely with reference to an example of embodiment and the appended drawings.